Preparation And Properties Of Glass Fiber Reinforced Polyamide 6 Microwave Absorbing Composites

With the development of the 5G era,electronic information technology is gradually applied to people’s life,and electromagnetic wave pollution also follows.Today,microwave absorbing materials are not only present in the military field,but the demand is also increasing in the civilian sector.The structural microwave absorbing material can ensure the mechanical properties while having the function of absorbing microwaves,which gradually overtakes the coated microwave absorbing material and becomes one of the hot spots of research.In this paper,the thermoplastic resin Polyamide 6（PA6）is used as the matrix,the continuous glass fiber（GF）as the reinforcement,and the acetylene carbon black（CB）,Kaolin（K）,and carbonyl iron powder（CIP）as additives of composites.CB/GF/PA6,CB/K/GF/PA6,CIP/GF/PA6,and CB/CIP@Si O₂/GF/PA6composites were prepared using a simple hot pressing process.The effects of the types and contents of additives on the microwave absorption properties and mechanical properties were investigated,and the microwave loss mechanism and the strengthening mechanism of the composites were analyzed.The results are as follows:（1）CB is a good absorber with good microwave absorption performance.The minimum reflection loss（RL）of CB/GF/PA6 microwave absorbing composites is-40.05 d B,the bandwidth of RL-10 d B is 4.6 GHz,and RL-5 d B contains the all Ku band.The granulation of carbon black can improve the microwave absorbing and mechanical properties of the composite.The minimum RL of the granulated CB/GF/PA6 microwave absorbing composite is-56.45 d B.The granulated CB forms a reticular conductive structure in the PA6 matrix,which increases the conductivity of the composite and improves the microwave absorption performance.In addition,the dispersion of CB in PA6 matrix can be made more uniform by granulation,which also provides a new method for the dispersion of nanoparticles.The GF enhances the mechanical strength of the composite,and the granulated CB increases the effect of particle reinforcement and forms a co-reinforced system with the GF.（2）The co-doping of CB and Kaolin led to the improvement of both microwave absorption and mechanical properties of the composites.The minimum RL of CB/K/GF/PA6 microwave absorbing composite was-59.78 d B at 10.15 GHz with a thickness of 2.5 mm,and the frequency range of RL-10 d B was 8.59～11.4 GHz,and RL-5 d B encompasses the entire X band.The special layered structure of Kaolin can make CB dispersed better,and the interface between Kaolin and CB also improves the interface polarization.However,when Kaolin and granulated CB are co-doped,Kaolin destroys the conductive reticular structure formed by granulated CB,resulting in a decrease in microwave absorption performance,indicating that granulated CB is not suitable for this system.（3）To prevent oxidation of the CIP,the CIP is coated with silicon dioxide（Si O₂）.The co-doping of CIP with CB can broaden the effective frequency band.The minimum RL of CB/CIP@Si O₂/GF/PA6 microwave absorbing composite was-26.79 d B at 13.99GHz with a thickness of 1.9 mm and RL-10 d B was 12.4～17.49 GHz.And the thickness of the composite at 1.91 to 1.95 mm,the RL-10 d B in the whole Ku band,which is wider than the effective band with only one absorber.The mechanical properties of the composites gradually increased with the increase of CIP@Si O₂content,but at the same time the mass of the composites also increased.The co-doping of granulated CB with CIP decreases both the absorption and mechanical properties of the microwave absorbing composites,indicating that granulated CB and CIP cannot be used together.